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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

The 97% consensus on global warming

What the science says...

Climate Myth...

There is no consensusThe Petition Project features over 31,000 scientists signing the petition stating "There is no convincing scientific evidence that human release of carbon dioxide will, in the forseeable future, cause catastrophic heating of the Earth's atmosphere ...". (Petition Project)

Science achieves a consensus when scientists stop arguing. When a question is first asked – like ‘what would happen if we put a load more CO2 in the atmosphere?’ – there may be many hypotheses about cause and effect. Over a period of time, each idea is tested and retested – the processes of the scientific method – because all scientists know that reputation and kudos go to those who find the right answer (and everyone else becomes an irrelevant footnote in the history of science). Nearly all hypotheses will fall by the wayside during this testing period, because only one is going to answer the question properly, without leaving all kinds of odd dangling bits that don’t quite add up. Bad theories are usually rather untidy.

But the testing period must come to an end. Gradually, the focus of investigation narrows down to those avenues that continue to make sense, that still add up, and quite often a good theory will reveal additional answers, or make powerful predictions, that add substance to the theory.

So a consensus in science is different from a political one. There is no vote. Scientists just give up arguing because the sheer weight of consistent evidence is too compelling, the tide too strong to swim against any longer. Scientists change their minds on the basis of the evidence, and a consensus emerges over time. Not only do scientists stop arguing, they also start relying on each other's work. All science depends on that which precedes it, and when one scientist builds on the work of another, he acknowledges the work of others through citations. The work that forms the foundation of climate change science is cited with great frequency by many other scientists, demonstrating that the theory is widely accepted - and relied upon.

In the scientific field of climate studies – which is informed by many different disciplines – the consensus is demonstrated by the number of scientists who have stopped arguing about what is causing climate change – and that’s nearly all of them.

1) Depending on exactly how you measure the expert consensus, it’s somewhere between 90% and 100% that agree humans are responsible for climate change, with most of our studies finding 97% consensus among publishing climate scientists.

2) The greater the climate expertise among those surveyed, the higher the consensus on human-caused global warming.

Expert consensus results on the question of human-caused global warming among the previous studies published by the co-authors of Cook et al. (2016). Illustration: John Cook. Available on the SkS Graphics page

Scientific consensus on human-caused global warming as compared to the expertise of the surveyed sample. There’s a strong correlation between consensus and climate science expertise. Illustration: John Cook. Available on the SkS Graphics page

Expert consensus is a powerful thing. People know we don’t have the time or capacity to learn about everything, and so we frequently defer to the conclusions of experts. It’s why we visit doctors when we’re ill. The same is true of climate change: most people defer to the expert consensus of climate scientists. Crucially, as we note in our paper:

Public perception of the scientific consensus has been found to be a gateway belief, affecting other climate beliefs and attitudes including policy support.

That’s why those who oppose taking action to curb climate change have engaged in a misinformation campaign to deny the existence of the expert consensus. They’ve been largely successful, as the public badly underestimate the expert consensus, in what we call the “consensus gap.” Only 16% of Americans realize that the consensus is above 90%.

Update

Comments

Rickoxo, if you say that the Earth has warmed and that humans have played a significant role, then you have to describe the mechanism. The only mechanism that fits those two conditions and the actual data is a large increase in atmospheric CO2. Once you understand what such an increase in atmospheric CO2 does (forces temp and ocean acidification), then you can factor in all of the feedbacks by applying the temp increase to all other climatological systems. The hard work is in figuring out the dynamic integration of these systems.

Accepting those two conditions in the question is, essentially, accepting the theory of AGW--as long as you accept the established physical model (Kirchoff, S-B, etc. ad nauseum). It is clear now, after decades of warming, that there are few negative feedbacks. Most are positive, including the big ones (albedo and water vapor).

It's possible that a major negative feedback awaits in the wings. Research suggests not. That wouldn't matter so much for the basic theory, though. It's warming, and we did it, and as long as we continue to do what we did and what we're doing, it will continue to produce the same physical response (worsening, of course). That's what 97% of climate scientists agree with. Indeed, if the question had been framed thusly ("Will an increase in atmospheric CO2 cause lower tropospheric warming?") then I imagine the percentage would jump to 99%.

I get that Doran (2009) is just one study, but we can't argue about every paper and every thread all at the same time, so it makes sense to me to see what Doran (2009) actually proves, especially since I had never heard of it before I got here and folks on this site brought it up and cited it as evidence.

DSL, I have no problem saying CO2 is a mechanism for warming and represents the significant role humans have played, I accept that 100% and I bet that most skeptic scientists would agree as well. The issue is the jump you're making from Doran's simple two questions (has the planet warmed since 1800 and have humans played a significant part) to your statement that accepting those two is essentially accepting the theory of AGW. Doran says pretty much what you said at the end of his piece, "It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes.

I agree that the planet has warmed since 1800, but agreeing with that does not in any way commit me to agreeing that humans caused the majority of that warming. The biggest flaw in Doran's survey is the wording of the human impact question. Having a significant effect does not mean anything about size. You said you were in ed research so you know tests for significance mean very little, effect sizes are everything. I get CO2 has gone up, I mostly get it causes warming but I am not convinced how much warming it's caused, what percent of the variance in temperature from 1800 till now has been caused by humans. Doran never asked this question so he has no grounds to speculate on an answer and when folks here cite the results from this survey as an example of agreeing with AGW science in general, that jump doesn't follow from the data. It could follow from all sorts of other places, but it doesn't get any support from Doran (2009).

When Doran said there is no debate over the role of played by human activity, he has no evidence for that statement. The wording of his human impact question is so poor that it leaves open all sorts of possibilities for yes answers on the survey that wouldn't at all indicate agreement with ICPP conclusions or even his own summary. Because he included nothing at all about the degree to which human activity is responsible for the warming since 1800, the degree to which human activity explains the variance in temperatures, just saying 90%+ of scientists surveyed agree that human activity deserves to be in the list of factors is not a helpful piece of information.

It says nothing about Doran being a fraud or dumb or anything, just that that survey question isn't useful in supporting the argument for a strong statement of consensus (like IPCC 2007). It also doesn't in any way imply there isn't consensus, it gives no evidence against consensus, but Doran (2009) is not evidence of a consensus of any significant position. If I were a scientist receiving this survey and unless I wanted to lie to thwart what I thought was the intention of the survey, I'd answer yes to both of those questions as well and I don't know of many skeptics that wouldn't as well. But when you have a question that doesn't reliably differentiate betweeen two fairly distinct groups of participants, it's just a bad question. And since we've never seen any of the other data and Doran says these are his two most important findings, it pretty much knocks out any usefulness of his study.

In the light of this site as a model of peer review, I saw a response to Doran by Murray Goot (http://www.garnautreview.org.au/update-2011/commissioned-work/the-%27scientigic-consensus-on-climate-change%27.pdf). The author made the same point I'm making, that the question is so poorly worded as to make it of little value, but the author goes on to give a broader lit review saying there's other evidence of consensus so Doran isn't necessarily wrong.

Again, I'm saying nothing about there not being consensus, I'm not saying Doran did fraud or anything bad. Writing surveys is incredibly challenging work and sometimes in writing questions, you come up with ones that don't actually give you the information you were hoping to get at. I'd love to see folks on this site get that Doran (2009) is fundamentally flawed and stop referring to it as evidence of consensus.

I think part of what you need to realize is that this need for scientifically establishing a consensus is itself a red herring.

People don't ask to see scientific proof that scientists believe that the genetic code surrounding ATCG is accurate, or that planets really have been discovered around other stars.

What we have is:

1) A branch of science where the people who work in the field know what is accepted and what is not to varying, imperfectly fuzzy degrees (i.e. normal science)

2) A group of people who have questioned the validity of the science because they don't like the answer

3) The fact that the vast majority of people in the field do accept the science and the conclusions as far as they go

4) A group of people who then take it a step further and question not only the science, but whether scientists actually agree about the science

5) A scientist who created a study to determine the strength and characteristics of any consensus

6) A group of people who then take exception to the study, insisting that it is invalid for various reasons (not a representative sample, not a well worded question, not applicable to the problem as a whole)

Do you see a pattern here?

Do you see this happening with any of the other thousands and thousands of areas of science?

My own opinion concerning your opinion is that if you don't trust the consensus or Doran, then do what the rest of us have done... read enough scientific papers to move beyond trying to water the consensus down to a yes no question and a percentage of respondents, and instead read enough of the current literature to realize how few people disagree and how many people do agree with each other's findings.

Personally, I do wish Doran would repeat his study to accomplish what you're asking. Make it a long questionnaire, with more specific questions and a larger population sample. But honestly, I don't see the point, and I don't need that degree of analysis to define the consensus for me, and I think that most people (I'm not saying you) who are requiring that sort of proof of consensus are just going to move on and add a point number 7 (and then 9, and then 11) to my list above.

Sphaerica, while I get the issue of consensus is a bit of a red herring, I think that consensus actually serves as a proxy for is the important question, is the science settled? Attempting to assess consensus gives us a window into that question.

I like your progression from 1-6, but I don't quite buy the pattern idea that it at least hits me you're suggesting. I had never heard of Doran (2009), it was cited here as evidence that scientist agree in the high 90% range with the basic premises of GWS. That is a simple proposition that can be evaluated apart from being a never ending progression of denial at every turn. It hits me that as part of the peer-review process of making sure only the best quality resources get cited as evidence for GWS positions, I'd think the GWS community would kick out the Doran paper because it so easily opens them up to criticism.

I partly picked the issue of consensus because it's more accessible to the non-scientist, I live in the world of grant writing and publishing so I have a lot of experience with some of the effects of consensus and I'm very curious about the proposition that the science is settled. Since I am not so capable (or have the time/energy) of going into all the science and determining its validity for myself, one of the ways I can partially address the question is look around in the community of experts to see the range of opinions expressed.

Pretty much no one questions whether or not we should teach systematic phonics to support beginning readers--the consensus is established, the research base is solid and it's pretty much a done issue. But figuring out the line from yes teach systematic phonics, but the exact methods, the amount of time per/day, the books that best support phonics instruction, all of those secondary questions aren't so settled. Some of what I'm hoping to see in the consensus debate are the types of questions experts in the field say are a done deal and the types of questions they say are still open to debate.

RickG, great cite, thanks for throwing it in. Wow, what a difference from Doran. Incredibly rigorous, careful, precise, hits me as a powerful study. Two things hit me most strongly in reading it, one, a slight problem with Anderegg's using publication frequency as a proxy for expertise, but the main thing, Anderegg's finding that 10% of climate scientists with at least 20 publications are unconvinced by the evidence for GWS.

The 2 second take on Anderegg's using publication frequency as a proxy for expertise is that I think every single journal in which these articles were published are put out by scientific societies that have made public statements asserting that GWS is a settled issue. I don't think it's a reasonable assumption that the likelihood of getting published is equivalent for both sets of scientists. At least in education, it's much easier to get published in a journal that agrees with the major tenets of your research than in one that disagrees with them, even though both journals are dealing with the same topic.

But the killer for me in this article, Anderegg came up with 90% in the convinced camp and 10% in the unconvinced camp (CE = 817, UE = 93), a hugely overwhelming and solid finding, but one that leaves 10% of climate scientists with at least 20 publications unconvinced by the evidence for GWS.

So try out this idea and tell me if it helps folks understand what I'm facing as a skeptic. I absolutely guarantee, bet every penny I have, that there wouldn't be 93 out of 910 physicists with at least 20 journal publications who don't believe Newtonian mechanics describes simple observable motion of objects. Those laws are easy to understand, can be empirically validated any time and there wouldn't be 10% of the physicist community saying objects don't accelerate when they fall or momentum doesn't = mass times velocity.

In the post on the homepage, "The Big Picture", Dana1981 wrote, "Sometimes people ask 'what would it take to falsify the man-made global warming theory?'. Well, basically it would require that our fundamental understanding of physics be wrong, because that's what the theory is based on. This fundamental physics has been scrutinized through scientific experiments for decades to centuries."

If this is the case, how can 93 climate scientists with at least 20 publications not agree with you?

Response:

[DB] So, if 9 cardiologists out of 10 said you need open heart surgery STAT, but the outlier said to take 2 aspirins and see how you felt in the morning, you'd be OK with that?

Similarly, if 9 out of 10 oncologists said you had a form of cancer requiring the most agressive course of chemo and radiation to survive, but the other one recommended some holistic therapy, you'd be OK with that?

Because that is what you are essentially saying: the outlier has equal credibility.

Rickoxo, be careful. You used Anderegg's term "unconvinced" early and then switched to "not agree." Your Newtonian example also devolves into an either-or (and only involves a single idea).

I'll wager that 90% of those 10% agree with much of the basis of AGW but are unwilling to commit for one reason or another. Spencer and clouds, for example. You can be unconvinced by the theories of Freud but also find a lot of truth in them.

As for the earlier complaint about the significance of the human contribution, it's up to the survey taker to interpret significance. If you don't trust the survey maker with the word, how do you answer? This does turn into an either-or if you do use the statistical measure of significance. CO2 is the control knob, and the human injection of atmospheric CO2 has been the difference.

You remain skeptical, though, based on the evidence of surveys. Surveys do not effectively measure the response to the complexity of the theory and, more importantly, its implications. If you're going to leave it at the survey level, then 90% should convince you. If I give you a 90% chance of winning a million dollars with a 10 dollar ticket, I don't think you'll pass the chance on to the next in line. If 90 people tell you you're about to get hit by a bus, and they all give the same reasons, and ten people tell you you're not but all their reasons are different, and some of the ten disagree with others of the ten, are you going to move your butt or keep sauntering? You can answer "I'm not convinced" with your academic mind, but your practical mind is screaming "move it!"

Better yet, though, just work out the basics for yourself. It only takes a few hours--less if you accept certain assumptions. If you accept the absorption spectra of the ten most populous atmospheric gases, and if you accept the evidence of rising CO2 concentrations and the mass balance argument, then you're halfway there. Just accepting those basics will, in fact, stop you from having to read probably half of the "skeptical" arguments rebutted on this site.

I will note that I'm with Sphaerica on this issue. Survey schmurvey. The survey still needs to be interpreted for the public, and the public has been well-trained to say, "yah, but it's just a survey and surveys can say anything." A survey certainly isn't going very far in the professional community. They make great copy for guys like Joe Romm, but he's largely preaching to the choir.

Rick. For the non-expert one way to see, literally see, the accumulated evidence is right here on Skeptical Science at History of Climate Science. Watching the evidence pile up on one hand, and the tiny assembly of other papers on the sidelines is striking.

As for "...the types of questions experts in the field say are a done deal and the types of questions they say are still open to debate."

The central issue is now and always has been the radiative physics of gases. This tells us what to expect for the atmosphere at eventual equilibrium.

The questions that are up for examination or needing further evidence are, by and large, about the transition period. I'd put them in 2 categories. One is about marching orders - what goes first and at what speed. Clearly the loss of Arctic ice has elbowed its way to the front at astonishing speed and shows no sign of slackening that pace. Floods, droughts, crop losses look, so far, to accord with expectations of the amount of warming so far in evidence. Things like major SLR, loss of icesheets and methane releases from clathrates are still in the 'could be a century or so, might be a couple of decades' basket.

The other category is 'work in progress'. Lots of this on transient sensitivity. Lots more for assembling and analysing data on OHC, feedbacks and the like. This category is also the 'more funds needed' and 'more time needed' group. If we'd had half a dozen more satellites collecting more and different data for more examination and analysis over the last 10 years, a lot of the topics people like to pick arguments about (eg clouds, aerosols) would already be done and dusted.

I think one important concept concerning both the Dorian and the Anderegg papers is that they stick specifically with the scientists who work and publish in the field. Conversely, what we see from the skeptic/denial side is signed petitions from people completely outside any field of research pertaining to climate science with little exception. I think it is also noteworthy to point out that the few skeptical papers that do get published are rarely with the mainstream journals and generally are reviewed by reviewers not in the field of those submissions.

As for the qualifying idea of number of publications and citations to one's credit, it is very significant. Experience does count and a paper that is cited by others numerous times indicates good work. Papers with no or few citations are generally of poor quality or contain little if any useful information.

Multiple strands of evidence from varied sources all leading to the same conclusion, as opposed to 'our club members all agree with other'.

As was said here, that's the only important survey: a survey of the evidence. Don't believe the results of what is basically an opinion poll? Spare us your opinion; show us the evidence the science is wrong.

"So try out this idea and tell me if it helps folks understand what I'm facing as a skeptic. I absolutely guarantee, bet every penny I have, that there wouldn't be 93 out of 910 physicists with at least 20 journal publications who don't believe Newtonian mechanics describes simple observable motion of objects. Those laws are easy to understand, can be empirically validated any time and there wouldn't be 10% of the physicist community saying objects don't accelerate when they fall or momentum doesn't = mass times velocity."

I think you've picked the wrong analogy with Newtonian mechanics. The reason for this is that, in the end, there are flaws in Newtonian mechanics and this was known at least at the turn of the 20th century. If you want to choose an appropriate analogy, you need to look at what supplanted Newtonian mechanics: relativity. When Einstein came out with his theories of relativity, it was something of a paradigm shift, much like the recent discoveries in climate science. A lot of people didn't like that. Including a lot of physicists (including at least two Nobel laureates). (There's an article in New Scientist but the text of the article can be found here. There's also a Wikipedia article.) Newtonian mechanics are, as you said, clear and easy to understand. Relativity, on the other hand, is non-intuitive and difficult to understand. It challenged people's notion of what the universe was like and people didn't like that. Reading about the relativity denial, it has struck me that there is a lot of similarity between them and the current climate change deniers. The relativity deniers complained that they couldn't get published because of a conspiracy by the proponents of relativity, just as we hear that scientists opposed to climate change can't get published due to conspiracies against them.

If you want to use a current analogy, I think you need to look at evolution. Like climate change science, there's an overwhelming amount of evidence supporting evolution. And, yet, you will still find plenty of people who deny it, even biologists, because it challenges their view of the universe.

Rickoxo @410, I think your interpretation of Anderegg is simplistic. You have assumed that for a given climate scientist who has published 20 or more papers, they are as likely to be included in Anderegg's survey if they are "Convinced by the Evidence" compared to if they are not "Convinced by the Evidence". That is a distinctly unsafe assumption. As is shown by the relative publication records of the CE and UE groups, only people with substantial records of achievement were included in the CE sample. In contrast, for those who are UE, no significant record of achievement was required, as is indicated by the high proportion of UE researchers with fewer than 20 publications.

The consequence of this is that we can be sure that nearly all UE researchers with 20 plus publications found their way into Anderegg's study. In contrast, there is a significant probability that CE researchers with 20 plus publications where not included in the study.

If we assume that the relative frequency of publication number is the same between the two groups, ie, that across all climate researchers, the proportion of CE researchers with 100+ publications relative to CE researchers with 20+ publications is approximately equal to the same proportion for UC researchers, then Anderegg's survey technique under represents CE researchers with 20+ publications by a factor of three or more. (This assumption amounts to the assumption that the greater "expertise" of CE researchers found by Anderegg is a function of greater numbers of CE researchers rather than of significantly greater intelligence.)

If that assumption reflects reality, then UC researchers with 20+ publications represent 3.65% or less of all climate researchers with 20+ publications. However, I do not think we are justified in drawing that specific a conclusion. The conclusion that they represent 10% of all climate researchers with 20+ publications seems far more perilous to me.

Still even with a 3.65% proportion, you might still be inclined to run your Newton argument. What that argument neglects is several key differences between Newtonian dynamics and climate science:

1) Newtonian Dynamics does not, as climate science does challenge some people's political ideologies;

4) Newtonian Dynamics does not, as climate science does challenge some people's economic interests; and

5) Unlike Newtonian Dynamics, there are several billionaires (and several billion dollar corporations) that will actively fund people to challenge climate science.

Given these clear sociological reasons for dissent, the proper comparison is not with a science like Newtonian Dynamics that challenges nobodies world view, but a science like evolutionary theory which as certain as Newtonian Dynamics, but challenging for many people.

I'd think the GWS community would kick out the Doran paper because it so easily opens them up to criticism.

I personally don't see the paper as part of GWS. It's published by a GW scientist, but it's social science. Maybe that's why it's weak, and a social scientist should tackle the issue.

Interestingly, that's what Wegman tried to do, too, to use social sciences against the consensus, implying that part of the consensus results from confirmation bias resulting from an old boy network among climate scientists. Interestingly, he used a network of his own friends to write his own report, and has been accused of grossly plagiarizing along the way.

But my whole point is "why all the emphasis on social sciences and confirming the consensus?" This isn't an issue with any subject except climate science.

Why? Because questioning the science won't work in this case, so questioning the scientists is even better. Sow mistrust and doubt.

This is a strawman. How do you jump from Newtonian mechanics, a hundreds years old foundation of physics, to cardiologists. How about instead whether or not cholesterol intake affects future heart disease?

It's an interesting parallel. There is a dispute over the efficacy versus dangers of the drug. The specialists, cardiologists, are primarily in agreement (I can't find the stats, but I'll bet it's only 9 of 10).

The FDA panel voted 12 to 4.

The general physicians strongly disagree!

What does this sound like to you?

And this example isn't perfect, because it's about a particular drug, with extreme (dangerous) side effects.

But what about statin's in general? I'll bet you'll find cardiologists that don't think they should be used, and even more general physicians in that camp. So... do you think people shouldn't take statin's to protect against heart disease? More important, do you see all sorts of studies that need to prove the consensus before people will buy into this whole, questionable "cholesterol" thing?

Response:

[DB] To be fair, I believe I introduced cardiologists (and oncologists) into the discussion as an analogy. However, having sold statins and Crestor to cardiologists, lipidologists and primary care physicians for years, you have the gist of it. The experts who are using advanced lipid testing are now able to parse out those individuals for whom statins will be ineffective much more readily than before. And Crestor's unique primary prevention indication is still limited to those individuals who still have normal lipid levels but a combination of other risk factors, thereby constraining its prophylactic use.

By now I'm waaaay off-topic & apologize for that. Moral: get advanced lipid testing done. It may save your life.

Sphaerica @417, the purported weaknesses of the Doran survey are entirely imaginary. The questions asked where phrased exactly the same as questions asked in a previous Gallop Poll. The idea was to compare expert opinion with public opinion, and that can only be done by asking the same questions. That does mean the Doran survey does not give us as detailed a break down on some issues as we would like, but just because research does not answer some of the questions we would like answered does not mean it was not effective research for answering the questions the researchers posed.

Rickoxo#410: "10% of climate scientists with at least 20 publications"

When did you establish that 'at least 20 publications' guarantees valid work? That qualifies Spencer, Lindzen (240 publications!), Svensmark, Akasofu ... as trusted experts. Why not look, instead, at the quality of their work, rather than the quantity? And do the same with the likes of Trenberth, Hansen, Rahmstorf, Schneider ... ?

Hint: That's hard work, but it is exactly the purpose of this site.

You say you're in education (as am I): How many surveys are there that directly contradict one another? One survey says class size must be reduced; another that students in smaller classes don't show higher levels of achievement. One survey says we must give more standardized tests; another says testing deters meaningful teaching.

A well-known climate 'skeptic' once responded to a question about the value of opinion polls with a scornful 'So?'

What an abundance of comments. Stepping back from the issue of consensus and GWS for a second, part of what I'm trying to find here is the nature of the argumentation. Again, I didn't bring up Doran, I had never heard of it, but it was used as evidence by people here that there is consensus. DSL, the word significant is not open to interpretation in research journals, it only has one meaning, and Doran knows what it is. The words of Doran's second question are exceptionally clear. But by asking about significance and not the strength of the effect, his survey gives no useful information. I would offer that the worst thing to do with a bad survey is attempt to "interpret" it so that it accomplishes what you wished it would have on its own.

I get there's a lot more evidence in favor of consensus and tons of evidence about GWS I haven't begun to look at, but for this piece, can folks admit its not evidence and doesn't support the positions of this site? If you want to ask skeptics to let go of arguments that don't support their skeptic position then folks here need to be able to let go of arguments that don't support the GWS position.

DB on Anderegg, so your question is totally valid and I completely agree (as well as with DSL's examples) that the huge bulk of evidence is on your side. I'm not debating that. A big part of what I'm trying to do in this thread is get at the question of consensus around the issue of the science being settled. Is there consensus on that and if so, what does that mean?

So here's what hits me as the critical issue. If the science is "settled" in the way I hear Dana1981 saying, then it is logically impossible for anyone to be a climate scientist who doesn't agree with GWS. The degree to which they disagree with GWS demonstrates their lack of expertise in climate science. There are no possible legitimate alternative interpretations of the data.

The other option is that 90% of climate scientists (according to Anderegg (2010) evaluate the current evidence and are convinced that GWS has the most explanatory power, fits the data most accurately and can answer the most arguments against it. But, 10% of legitimate climate scientists aren't convinced of that and have evidence-based reasons why not. Their disagreement doesn't indicate a lower degree of expertise. They could be less expert for all sorts of other reasons, but disagreement with GWS doesn't indicate lower or complete lack of expertise.

The big difference between the two and why I chose Newton's laws as an example, in option 1, disagreeing with F = MA for simple motion (I'm not talking about relativistic motion) demonstrates you don't know physics and everyone who knows physics knows that. In option 2, the climate scientists who are in the 90% camp can understand the logic and reasoning of the 10% scientists, they don't consider them frauds, myths peddlers or oil company shills, they get that the evidence is not entirely conclusive and there are legitimate alternative explanations, albeit ones that the huge majority of the climate science community finds unconvincing.

But those are sooooooooo different. At this site, it mostly seems like group 1. How do you know if someone is a legitimate scientist, they accept GWS. Anyone who doesn't is a myth peddler.

So, can a legitimate climate scientist look at all the evidence currently available, and come to a scientifically valid conclusion that disagrees with IPCC? Again, I'm not talking disagreeing that the planet has warmed since 1800 or does CO2 affect the climate. But let's say with the single premise, "we can quantify the amount of warming human activity is causing, and verify that we're responsible for essentially all of the global warming over the past 3 decades?" Could a legitimate climate scientist disagree with that statement and not be a fraud, myth peddler or oil company shill? Could other climate scientists who think we have caused all the warming look at the reasoning used by the skeptic and agree that it is valid reasoning because the data are not entirely conclusive?

Sphaerica, I'm not at all saying that Doran has anything to do with climate science. Both he and Anderegg did a great job of saying their papers were about describing the state of the field and added nothing to the research base on climate science. I'm not saying anything different if that's what you're pointing out.

But what I was trying to say in the quote you cited was that Doran (2009) was given by people at this site as evidence of the GWS position that there is overwhelming consensus for GWS science. I haven't disproved anything about actual science, but Doran's wording is too simple to argue against. "Do you think human activity is a significant contributing factor in changing
mean global temperatures?" He didn't say which direction, he didn't define human activity and significant contributing factor says nothing about how much of a factor. In academic writing, significant is a term with precise and unequivocal meaning, it is not used in the more common place sense of important or substantial. Tests for significance are important in research and knowing that human activity is a significant contributing factor is great, but it says nothing about the degree to which it's a contributing factor or the role played by human activity in climate change.

When Doran writes that debate in GWS over the role played by human activity is non-existant, that might be true, but he didn't provide any evidence for that statement. He could cite someone else, Anderegg maybe, but he didn't give evidence in favor of that statement.

It's no big deal to do a bad survey or to have to chuck pieces of evidence that was supposed to argue in favor of your position but doesn't turn out to in the long run. It's a big deal if the peer-review community tries to say that a bad survey is still legitimate because the idea it's saying it found evidence for is corroborated in other places.

I get that the quote at the end of Doran, the one about the debate being non-existent is a powerful quote, it's well written, it's clear, it's direct and it might even be true. But he didn't provide evidence it was true so to cite him as evidence opens you up to getting ridiculed for citing bad research in support of your positions.

rickoxo@422: "How do you know if someone is a legitimate scientist, they accept GWS. Anyone who doesn't is a myth peddler."

You continue to frame the argument in a manner that is entirely backwards.

One is not a myth-peddler simply by 'disagreeing with IPCC.' One os a myth-peddler because one peddles myths.

In this quest, you've missed the fact that this site challenges the work of those it labels myth-peddlers. When fault is found in their work, those faults are called out. Those who continually publicize conclusions based on work identified as flawed (or even false) are the myth-peddlers. What is shown time and again to be settled is the weight of the scientific evidence, not necessarily the scientific opinion. But in science, opinions don't carry much water.

But you then pose the question a tad differently:

""we can quantify the amount of warming human activity is causing, and verify that we're responsible for essentially all of the global warming over the past 3 decades?" Could a legitimate climate scientist disagree with that statement"

That's a new, vastly higher hurdle; some no doubt can and do disagree with your words 'quantify,' 'verify' and 'essentially all'. The IPCC statement typically quoted is not at all the same:

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

I find it fascinating that you've analyzed what is a higher-order science (one that is composed of parts from many disciplines - and therefore brings all of their uncertainties) through the lens of opinion polling, a kind of 'meta-knowledge' that does little more than introduce its own uncertainty. Its a bit like trying to measure a very long distance, not by using a meterstick (difficult enough), but by using a stick of uncertain length.

Very good arguments. There are those (especially here) that will point to the Doran survey and claim that 97% believe in AGW. I cringe every time I here that. As you have detailed, the survey is quite vague, and the paper should not used as evidence for a consensus.

The further problem with poeple using consensus is that they confuse what actually makes up the consensus. Yes, a vast majority agree that the planet has warmed and that CO2 is a greenhouse gas. The divergence occurs when asked, "how much?" You have alluded to this point quite well. While 90% may believe that we humans are warming the planet, how much we are warming the planet is very much open to debate. There are those you will jump from the Doran survery (or Anderegg) and claim that those same scientists who believe that CO2 is a greenhouse gas also believe that the claims of large positive feedback and exponential warming. This is were the consensus breaks down, with a wide array of beliefs, each supported by scientific research. We currently have an "average" value of warming.

Of course, muoncounter says it best, "in science, opinions don't carry much water." Whether 97, 90, or whatever believe in something does not necessarily make it true. Science is based on research, not opinions. This is not to say that it is not ture, but only that it does not supply evidence of its truth (either way, as you explained).

"There are those you will jump from the Doran survery (or Anderegg) and claim that those same scientists who believe that CO2 is a greenhouse gas also believe that the claims of large positive feedback and exponential warming. This is were the consensus breaks down, with a wide array of beliefs, each supported by scientific research. We currently have an "average" value of warming."

For what it's worth, the Anderegg 2010 is neither a survey nor a poll and should not be associated as such. I also think it is important to realize that probably none of those consensus studies would have been conducted had the skeptic/denial side not stooped to the level of deliberate misinformation by compiling huge lists of climate change skeptics who were "scientists" but not climate scientists; but nevertheless suggesting they somehow have some expertise in the area.

Rickoxo, EtR raises an interesting point, and one that I tried to address earlier. He says, "the divergence occurs when asked, 'how much?'." This is the problem with asking about significance in this context. If humans are warming the planet, what does significance mean? Are you measuring over a day, a year, a decade, a century? If we get just a 1C global average increase just from CO2 per century, is that significant? If you say no, a thousand years from now you might say yes. If the effect of our aerosols masks that increase, is the effect still significant? Nature is trying to cool the Earth right now (orbital slightly and solar), so what do you measure significance from? The natural trend? The most recent climatological period? Pre-industrial? Significance is not a simple question here. There are also some who might answer the question thinking, "Well, we've hit peak oil, and emissions will soon decline, and we'll end up mitigating, so while we could, we'll never really hit the IPCC's middle-of-the-road scenarios, so I'll answer no." Yes, Doran knows what statistical significance is, but the survey question doesn't limit the conditions of significance.

At this point in your travels into climate science, what would you answer to both Anderegg and Doran? And what is the confidence level of your answer?

If you want to find out why there is not a 100% consensus, go to the publications. Ask Anderegg which scientists he found who did not demonstrate support for the theory. Ask Doran for the names of the 2.5% of climate scientists. Look at their reasons, their publications. You will then know why the claims of consensus are accurate. You'll gain environmental (contextual) knowledge that many of the posters here already have but that outsiders (survey readers) don't have.

And now you see why it is so difficult to communicate the science to non-scientists--and why it is so easy for those who are motivated to do so to obfuscate, misinform, generate doubt, and generally stop we, as a whole, from doing anything about the growing problem.

" The divergence occurs when asked, "how much?" You have alluded to this point quite well. While 90% may believe that we humans are warming the planet, how much we are warming the planet is very much open to debate. There are those you will jump from the Doran survery (or Anderegg) and claim that those same scientists who believe that CO2 is a greenhouse gas also believe that the claims of large positive feedback and exponential warming. This is were the consensus breaks down, with a wide array of beliefs, each supported by scientific research. We currently have an "average" value of warming."

I know you would like this to be true, and you have asserted it on several occasions. They only thing lacking has been the evidence.

Let's take scientific opinion first. Among climate scientists 62.01% think the IPCC accurately estimate the magnitude of future changes of temperature. A further 15.64% think the IPCC slightly under estimates the magnitude of future temperature changes, while 11.73 think that they slightly over estimate them. That means 89.93% of climate scientists think IPCC estimates of future temperature changes are accurate or only slightly inaccurate. A further 4.47% thinks the IPCC significantly under estimates future temperature changes, leaving just 6.15% who think they significantly over estimate those changes. Those figures are hardly signs of a consensus that has broken down.

That means that there is a consensus (>90%) of climate scientists who believe the temperature increase for a doubling of CO2 is likely to be between 2 and 4.5 degrees C, a figure that is dangerous at anywhere in that range.

Indeed, that is something the climate scientists also agree on, with over 60% being strongly convinced that climate change poses "a very serious and dangerous threat to humanity", with a further 31% being moderately convinced of that claim. Just 6% significantly doubt that possibility, and from those 6%, only a third are completely unconvinced of any danger.

DSL, I don't think I have any basis for an assessment of the science yet, I'm still trying to get a handle on what the experts in the field believe. At some point I'll pick an aspect of the science and get as into the detail of that as I can, but for now, getting a sense of the degree to which experts in the field see the science as settled or open to debate but clearly leaning in a direction hits me as a useful starting point.

I get that Doran didn't define the context under which he was asking about human contribution to climate change being significant, that's one of the flaws in his survey, but that still wouldn't change the meaning of significance once he defines the nature of the contribution he was talking about.

I didn't mean to try for a higher standard, I was just trying to pull out what hit me as a clear and critical premise from IPCC so we didn't get bogged down in questions of, "well this person disagreed because of the policy issues, and this person disagreed because of something else, etc."

I got that quote from here on this site and now looking back, I see I didn't give a reference, sorry for that. The quote comes from Dana1981 in the big picture post that's linked on the home page, end of the 2nd sentence in the "Humans Are Causing the Warming" section. I used that quote because I thought it reflected a reasonable summary of the opinion at this site and I thought it reflected what IPCC said as well. Sorry for the error on my part.

I appreciate your comment, "That's a new, vastly higher hurdle; some no doubt can and do disagree with your words 'quantify,' 'verify' and 'essentially all'."

I find it interesting that this site is promoting a statement of GWS that is stronger than the IPCC position. In that same section of Dana1981's post, he answers the question of what would it take to refute man-mad global warming theory, "it would require that our fundamental understanding of physics be wrong, because that's what the theory is based on. This fundamental physics has been scrutinized through scientific experiments for decades to centuries.

It's this kind of combination of extremely strong statement of GWS linked with a claim that the evidence is so overwhelming that it's basically beyond refutation that makes me think this site is expressing more personal opinion than summary and distillation of what the scientific community would say about this topic. I'd bet everything I have that if those two sentences from Dana1981 were on the Doran survey, there wouldn't be anything near 90% acceptance of both of them. Yet those two sentences are presented in a featured article on the home page of the site.

p.s. back a comment or so ago, I didn't set up the criteria from 20 publications as indicating sufficient status as a climate scientist, that comes from Anderegg

Rick "At some point I'll pick an aspect of the science and get as into the detail of that as I can..."

'An aspect' encompasses many things. If you're looking at the central issue - the radiative physics of gases - all well and good. That's where the core science is, that's where the agreement is.

Don't pick a side issue or a fine detail like droplet sizes affecting albedo of clouds (and dozens and dozens of similar nitpicks).

The item that's been so competently put together relies on radiative physics in the atmosphere. The fine details are important for getting the best presentation possible - but the garnishes, crockery and cutlery don't change the fact that a meal is ready to serve. Changing the colours of plates or shape of forks might improve the look but not the nutritional content or the taste of the food.

If, like me, you're not a scientist, concentrate on learning the basics. Be warned, basic does not mean simple or easy or quick. Science of Doom is probably the best place to start for digestible serves of serious science.

And if you don't get into the science, Rickoxo, then you're going to be left relying on opinion. If I point out that some of the minority do their publication in dodgy journals, you'd have to take my word for it. Adelady's advice is good, but wear your math hat at SoD. The Miskolczi series is interesting if you like to see the in-depth interrogation of one of those 10%. If you're into the statistical side, Tamino gives statistical silliness the baseball bat treatment. It's a no-brainer over there right now, though (Joe Bastardi).

Rickoxo#430: "... makes me think this site is expressing more personal opinion than summary and distillation of what the scientific community would say about this topic."

No one here pretends to speak for the 'scientific community.' I doubt that many here would take issue with Dana's stronger statement ('... require that our fundamental understanding of physics be wrong'). It takes some understanding of both the physics and the intricacies of climate science to be able to say that with confidence.

A statement such as the one in IPCC AR4 ('... very likely due to observed increase in anthropogenic greenhouse ...') is clearly a watered down, committee-written compromise version of what they could have (and probably should have) said. You can only see that and begin to grasp the fullness of the problem by learning something about the science. Relying on what can only be described as 3rd hand information is a very dangerous practice because there are lots of bad sources out there (and they very often come here to promote their uninformed opinions).

Dana69 @11:39 AM, 13 September, no. Over the course of the 20th century natural phenomenon have contributed slightly to the warming. However, over the last 30 years, natural forcings alone would have resulted in a slight global cooling.

On the other hand, anthropogenic global warming would have been much stronger without the effect of human emitted aerosols which cool the Earth and have countered as much as half of the overall warming trend, and in some periods (eg 1950 to 1970) have almost completely countered the warming trend.

SO it seems fair to say that there are arguments for both sides of the equation.

To be sure about my skepticism: It is necessary for me to see and examine the arguments of both sides of the fence, and I then make up my own mind, based on these arguments.

I am pretty sure that current climate models underestimate the role of the sun in climate variability and overestimate the role of greenhouse gases and aerosols. But I am as sure that the increase of CO2 in the atmosphere since the start of the industrial revolution is mainly from the use of fossil fuels.

Appealing to authority that there is 97% consensus is a fallacy.

Quick thought experiment. Lets say your a physicist that has been in a coma for the last 40 years. You wake up to the current world and the first headline you see is the shrinking arctic ice. Someone walks by and states how could anyone doubt that man is not destroying our world with CO2. You ask the person what she means and she says that 97% of all scientists claim there is a consensus regarding AGW.

Would this physicist run around and defend the point by claiming 97% consensus? If his mother asked him about the proof, is his quack, consensus, consensus enough?

Response:

[DB] "It is necessary for me to see and examine the arguments of both sides of the fence, and I then make up my own mind, based on these arguments."

Try starting here and reading up on all of the argument rebuttals that interest you.

"I am pretty sure that current climate models underestimate the role of the sun in climate variability and overestimate the role of greenhouse gases and aerosols."

Dana69 - based on the questions you are asking, sitting down with the IPCC AR4 would be a good first step. Know what the published science is and then take it from there. I'm looking forward to you presenting evidence for science underestimating the sun. Perhaps you should look at Benestad & Schmidt 2009 found.

dana69#437: "a physicist that has been in a coma for the last 40 years."

I suspect there are a few of those around. However, the flip side of your question is equally valid. Does Rip Van Physicist side with the dissenting 3%? Or does he infer that there must be an enormous weight of evidence behind the opinions of the 97%?

Being skeptical is certainly the right approach, but giving equal weight to all arguments is not. You will find that there is a very clear correct answer to almost every issue in climate science, no matter how much doubt certain people attempt to sow. A lot of people will lead you astray with seemingly sensible but incomplete analyses (such as your chemist friend's discussion of how CO2 warms the atmosphere).

To begin with you will very quickly learn that (a) it absolutely is not the sun and (b) there is absolutely no question that the rise in CO2 is 100% the result of human activity, and the majority of it is from burning fossil fuels.

I would also point out that argument from authority itself is not a fallacy. The fallacy occurs when the authority is not qualified in the area in question, or when the point is expected to be taken as 100% true because of the authority's position.

But it is perfectly valid and common to use the position of an actual, qualified authority when one is not and cannot become completely educated in a matter themselves. As with much of science, very little is ever taken as 100% true, but much like the consensus discussed on this thread, for all intents and purposes the probability of truth must govern reason. It's simply not logical to say "it seems almost certain that what I'm doing will kill me, but it's not 100% certain, so I'm going to go ahead and ignore the risks."

... or does Rip Van Physicist (assuming his 40-year coma has not had too many ill effects) actually go and read some of the key papers and get to grips with the overwhelming nature of the evidence, rather than basing it on somebody else's survey-based opinion?

I'm also interested to hear where solar activity has been underestimated and CO2 been overestimated.

Dana69 wrote: "It is necessary for me to see and examine the arguments of both sides of the fence, and I then make up my own mind, based on these arguments."

well quite, that is what we should all do. Have you read the IPCC WG1 report (or at least used it to check whether claims are true)?

However Dana69 then wrote: "I am pretty sure that current climate models underestimate the role of the sun in climate variability and overestimate the role of greenhouse gases and aerosols."

I suspect that you have not done enough reading to have a balanced view on this one. Please go to "Its the sun" and give a list of the sources for and against on which you base your opinion and then give an explanation of why you think the models do not sufficiently account for the role of the sun. I will happily discuss this with you if you can show that you have followed the procedure you have set out in the first quote.

As for Rip van Scientist, he wouldn't defend any position until he had had a chance to get up to date with the science (fortunately the IPCC has produced a report which sets out the mainstream scientific position, the NIPCC have similarly produced a report setting out the contrarian view). He (being a scientist) would then base his arguments on the science.

The importance of a concensus is not of any relevance to the scientists, who are capable of grasping the scientific arguments. Its importance is for the rest of us who can't accurately weigh the scientific arguments becase we don't have the necessary background. Then like seeking second (and third, and fourth and ... n-1th and nth) opinons for a medical problem, the fact that a strong majority recommend a particular course of treatment is a fairly reliable indication that it would be a wise course of action.

Good science generates broad (but never complete) concensus, not the other way round.

Roh: "And in the Oreskes report he took a poll in 'refered journals'. There has been rejection of skeptic papers in the journal as it 'goes againt the consensus'."

Roh, you really don't understand how journals work, do you? You assume there's pressure on journals to adhere to the consensus. Why? What's the mechanism? If anything, there's pressure not to adhere to the consensus. Who would want to reject a paper because it "blows a hole" in the dominant theory? That's the kind of stuff that Science and Nature salivate for. In reality, though, there's simply pressure to get the science right, whatever it might mean for our understandings. Don't you agree?

Consensus is based on science, but science is not based on consensus. Consensus is a political argument, not a scientific argument. The scientific process is based on evidence, not consensus. Scientific evidence does not care about any consensus.

Consensus does not imply that the science is correct. To argue otherwise is to commit these two fallacies:

That, in a nutshell, is why scientific "truth" is not determined by consensus, but rather by evidence.

Here are some recent examples of the scientific consensus being wrong. Each of the following examples were initially rejected by the consensus, but the consensus changed based on evidence.

the theory of continental drift
the theory of symbiogenesis
the theory of punctuated equilibria
the theory of prions
the theory of Helicobacter pylori as the cause of stomach ulcers.

Consensus is based on scientific evidence, but consensus itself is not scientific evidence. Consensus is merely a statistical survey of scientific opinion. It is not a guarantee that the scientific opinion is correct.

Settled science claims are inductive arguments which assumes the number of scientists who agree strengthen then argument.

While induction does not strengthen the argument scientifically,it does strengthen the argument in a rhetorical sense. Consensus is a rhetorical (political) argument, not a scientific argument.

Politics relies heavily on consensus. Science does not. Policy decisions ought to be made on the best available information,and in that sense only is consensus valuable.

For the record -- in anticipation of possible misinterpretations of my position on global warming -- I have not attacked the scientific consensus. I have not denied there is a consensus where there truly is a consensus.

I have however, attacked claims of consensus where there is no actual consensus. And I have simply pointed out that the consensus argument is not a valid scientific argument. And that it depends on which scientists you choose to believe. But I am not attacking the consensus that the Earth is warming.

1) Do you agree that most of the observed warming the past 100 years is from humans burning fossil fuels?
2) Do you deny the theory (it is no longer a hypothesis) of AGW? That is, do you deny the physics behind it?
3) Do you deny the body of evidence consistent with the theory across many scientific disciplines?

Please make your position very clear, and perhaps the best way to do this is for you to state what you believe the equilibrium climate sensitivity is for doubling CO2. A number please with 95% confidence limits.

Dana69 "And I have simply pointed out that the consensus argument is not a valid scientific argument. And that it depends on which scientists you choose to believe."

Nature does not choose to believe any opinion, it is physics, chemistry, biology etc. And the observations, across many disciplines are perfectly consistent with the theory of AGW. So on that note, instead of railing against "consensus", you should really be railing against "consilience".

As for consensus, you know what is intriguing Dana69? The reason that consensus on AGW came to the fore was because "skeptics" and those who deny AGW were claiming that scientists do not agree on the subject. How does one address that? You show them that scientists are in agreement, that the body of evidence and observations across many scientific disciplines are consistent with the theory of AGW. What does the "skeptics" then say,

"Well, consensus is based on scientific evidence, but consensus itself is not scientific evidence. Consensus is merely a statistical survey of scientific opinion. It is not a guarantee that the scientific opinion is correct."

And so the faux debate continues. "Skeptics" have had since the days of Fourier, Tyndall and Arrhenius to overturn the building blocks of AGW, and have not...so in lieu of making substantive scientific arguments they have to resort to playing games.

Dana69 Pointing out that mainstream science has been wrong on occasions before where there has been concensus does not mean that the existence of a concensus on AGW tells us nothing about the likelihood of AGW being correct. To make such an inference you would also need to consider the number of occasions where there has been a scientific concensus on some issue where the concensus has been correct.

The solidity of the science is what causes the concensus, not the other way round, you are correct to point that out. However a corrolary of that is that the existence of a concensus is usually a pretty good indication that the science is solid.

Thus while the existence of a concensus has no bearing on whether the science is actually correct or not, it is completely rational to take the existence of a concensus amongst the experts as strong evidence that the science is solid, and that it would be wise to be primarily guided by mainstream science rather than scientific "outliers" when deciding on a course of action.

First off, let me tell you I have been very impressed with your posts here,and in forums off this site. I am not sure what your background is, but it appears to be solid in statistics.

Please understand my post. I have indicated agreement that the climate is warming. This notion of consensus to validate a point is useless. If the consensus hasn't done the work then it is simply appealing to Argumentum_ad_populum.

If the argument can be made scientifically, then appealing to the fallacy of consensus is unnecessary and irrelevant. Scientists do not need to point to a consensus, they simply point to the facts and the evidence. So why bother using consensus as an argument at all?

Since most of the scientists signing on to the AGW "consensus" are not climate experts -- in fact even among climate experts they are not all expert in each others specialty -- Dr. Trenberth for example is not a hurricane expert -- it appears that the consensus is saying it is not based on the scientific method but rather on popularity.

Consensus seems to mean, "I have looked at your results and even though I have not personally verified those results or even looked at all your data, it is my personal opinion they are probably valid."

I'm sorry, but that is not the scientific method.

Basing one’s beliefs on the scientific consensus is rational. I do it often. It is not the only rational response, however. It is not irrational to be skeptical of an argument based only on consensus.

Secondly, and perhaps most importantly, there is no scientific consensus on what the political response to AGW should be.

Dana69 I think you are missing the point of the significance of the concensus. The science doesn't stand and fall on the existence of a concensus. Similary those who can reliably understand the science can happily ignore the existence of the concensus. What about the rest of us who are not capable of reliably understanding the science at the level of detail required to form an opinion of our own (I most certainly fall into that category). We have to decide where the truth is likely to lie via other means, and the existence of a concensus is a useful indicator of reliability of expert opinion. If you are ill, do you trust your doctor or do you go and do the research you need to do to diagnose yourself? Most of us do a mixture of the two, but heavily biased in favour of the doctors opinion because he has earned hid credibility, we haven't. Now logically this is "argument from authority" and thus a fallacy; however it is also perfectly reasonable and rational. No it isn't science, but like the AGW debate we are fooling ourselves if we think we are doing science. We aren't, merely trying to understand and interpret the science of others so that we can hold an informed opinion.

It would be a logical falacy to say that the science is right because there is a concensus. That would indeed be "argumentum ad populum". However, it would be perfectly correct, to say that it was more rational to have confidence in the concensus position than in the skeptics; on the balance of probabilities (not certainties) you are very likely to be right.

The concensus says nothing about the actual correctness of the science; it says plenty on how we (as non-experts) should rationally apportion our belief to the competing hypotheses.

"So why bother using consensus as an argument at all?"
I've explained why to you above @443.

I'm sorry Dana69, but you really are saying an awful lot without really saying anything. That is why I was asking you to answer some specific questions to try and determine where you are coming from.

You say "it appears that the consensus is saying it is not based on the scientific method but rather on popularity."

Let me remind you about the purpose of this post, the main post was made to address this claim made in a petition:"The Petition Project features over 31,000 scientists signing the petition stating "there is no convincing scientific evidence that human release of carbon dioxide will, in the forseeable future, cause catastrophic heating of the Earth's atmosphere"

The goal of that petition is to advance the claim that there is "no convincing evidence" for AGW and that that opinion is held by many people with credentials. Well there is compelling evidence, from multiple, independent lines of evidence in fact. You talk above about "popularity", well such petitions are just that, and worse yet, signed by people not qualified to speak to the subject. Do you endorse such petitions as a refutation of the theory of AGW? I hope you agree that such an approach is not the scientific method, unlike how the theory of AGW was arrived at.

"Since most of the scientists signing on to the AGW "consensus" are not climate experts"
Not true. Please read Anderegg et al. (2010) a link is provided in the body text. Please note the tiny fraction of people who sign petitions wishing away the theory of AGW are qualified to speak to climate science. Is that OK by you?

"Since most of the scientists signing on to the AGW "consensus" are not climate experts -- in fact even among climate experts they are not all expert in each others specialty -- Dr. Trenberth for example is not a hurricane expert"

I'm sorry, this is an absurd point. But it does underscore why consilience is so important. Trenberth has shown that the water vapour content of the atmosphere is increasing as temperatures increase, that is a positive feedback that is key to the theory of AGW and perfectly consistent with the Clausius-Clapeyron equation. Whether or not he has experience to speak to how hurricanes will respond to a warming planet is not relevant, and besides, how hurricanes respond to a warmer planet has nothing to do with the validity of theory of AGW.

So I'm sensing some strong one-sided skepticism here by you Dana69. Lindzen is a meteorologist by training, so by your logic he is simply subscribing to popular opinion when he agrees that doubling CO2, in theory, will warm the planet by 1.1 C or so.

Dana69 wrote : Each of the following examples were initially rejected by the consensus, but the consensus changed based on evidence.

the theory of continental drift...

Well, it's hardly surprising that it was rejected, when Wegener believed that the physical processes involved were to do with the rotation of the earth or gravitational attraction involving the sun and moon. Would you have believed that ? I doubt it, because the calculations didn't add up.
It was only when the theory of Plate Tectonics was refined and provable, and the forces involved were undestood to be thermal convection currents within the mantle, that the original theory (albeit adapted) could be accepted and proved.
How does that compare with the theory of AGW ? Is there another theory out there that you think might be better ?

Dana69: "even among climate experts they are not all expert in each others specialty ... it appears that the consensus is saying it is not based on the scientific method but rather on popularity."

This argument is very strange. Would it be better if most climate scientists - whatever their specialty - disagreed with the important elements of a theory? Seems to me that if that were the case, you'd be arguing 'there's no agreement among scientists!'

It is also most often the 'pseudo-skeptics' who bring up this consensus issue. Those who have looked at evidence objectively seem content that many independent lines of evidence point in the same direction. That's the consensus worth talking about.

Sorry for taking so long to answer your questions posed @447. Just for the record this thread is regarding consensus; my views regarding any particular point is not relative to this topic. If I am to follow the conclusions of the so called "consensus", any meaningful result would have naturally stemmed from the consensus itself, and not my own views. It becomes circular.